Greenhouse Management: Can hemp growers utilize mycorrhizae, and if so, which strains should they be using?

Blair Busenbark: First of all, I think hemp growers have been using mycorrhizae for many years. It is important that hemp growers use endo-mycorrhizae strains because they are endo plants.

Scott Inman: Hemp and other plants in that genus utilize arbuscular mycorrhizal fungi, which are a very generalist mycorrhizae. They colonize over 80% of the world’s plants, and there are roughly 400 identified isolates. One associates with a lot of different plants, but it’s also driven by environment, plant type and soil type, as well as the conditions under which the microbes develop. The plant is the driver of this relationship. It’s a true symbiotic relationship so the plant is the one turning on and off the mycorrhizae. That’s a key component of this association for growers to keep in mind.

GM: What benefits do most hemp plants receive from mycorrhizal fungi?

SI: It depends on the conditions. If you look at the different hemp growing segments and what those growers are doing, the big one is nutrient availability. A lot of nutrients are tied up in the soil and require some level of microbial activity. And it’s also a stress mitigation — it allows the plants to have better access to water and nutrients to help mitigate stress.

BB: I would add that it is important to realize that the stresses the crops can undergo themselves are different. It will experience different stressors whether the crop is grown in Texas or Kentucky or even in New York State. And so, the plant is driving what benefits it is getting from the mycorrhizae, and then you throw on top of that the different production protocols and variables — how they are irrigating, how they are fertigating and all the different varieties — you throw all those variables together and really the overall benefit is that it helps the plant be more successful in a wider variety of situations.

GM: What are some tips for growers in how they can incorporate mycorrhizae into their production system?

BB: When you look at how hemp is produced for the high CBD markets, most of those crops are being started in greenhouses and then transplanted outdoors. All of those crops can have a drench as well as a soil incorporation to add the mycorrhizae, that’s a simple way to do it. And then keep in mind that mycorrhizae only need to be applied once during the production cycle, so if you apply it during propagation it will stay with the plant through transplant, and it will continue to benefit the plant throughout its life cycle.

Greenhouse Management: What factors should growers keep in mind when selecting a water-soluble fertilizer?

IB: Crop specificity is the first one. Experienced growers know that crops like tomatoes, cucumbers or lettuce require different proportions and concentrations of essential plant nutrients to thrive. Photoperiodic crops like chrysanthemums or poinsettias prefer lower levels of nitrogen during flower, where phosphorus and potassium management is critical.

The next factor to focus on would be product purity. Nutrient salts are predominantly mined from the earth. The mineral deposits are then purified and graded. For producers growing edible or medicinal crops, the purity of inputs is critical to ensure hazardous heavy metals are not making their way into the finished product.

And lastly, consistent product performance should be emphasized in the product selection process. None of the above matters if your fertilizers are not mixed, proportioned and manufactured to the highest of standards. This is critical because growers spend considerable time and effort perfecting their nutrient recipes to best support their crops growth and development.

“Experienced growers know that crops like tomatoes, cucumbers or lettuce require different proportions and concentrations of essential plant nutrients to thrive.” -Ian Bateman

GM: How do growers dilute/concentrate water-soluble fertilizers?

IB: Water-soluble fertilizers must first be dissolved in water prior to applying to your crops. There’s two primary methods growers use to prepare a dilute, ready-to-use nutrient solution using water soluble fertilizers.

For growers using reservoirs, start by filling water to the final volume in your reservoir and measure out the appropriate amounts of water-soluble fertilizer. Begin adding fertilizer(s) to your reservoir one at a time, while stirring or agitating the water. For multi-part fertilizers, always add the fertilizer that contains calcium first.

To prepare a concentrated nutrient stock solution for use with fertilizer injectors, start by filling water levels to 80% of the desired volume in your clean stock tank. Always use Reverse Osmosis (RO) or low Total Dissolved Solids (TDS) water. Next, measure out the appropriate amounts of water-soluble fertilizer and add it to the stock tank. Generally, it is best practice to allow for each water-soluble fertilizer to occupy its own stock tank.

It is important that you never combine calcium containing fertilizers with sulfate or phosphate containing fertilizers in the same concentrated stock tank, as precipitation will likely occur. Mix with a paint mixer or paddle style mixer for best results, hot water will greatly speed up the dissolution process.

Greenhouse Management: Why is it important to combat root infecting diseases early on?

Joe Lara: Root diseases require a lot of attention because when the plants are at a young age and are just getting started, they are very susceptible to diseases. When growers start these plants, they have from thousands and up to millions of dollars invested. If they can’t get that crop going early on, they end up with low yields, poor quality plants and significant setbacks. Because of this, growers are really working hard to advance their approaches to disease control in general, utilizing all the tools available to them with integrated pest management. BioWorks has been a leader in developing these high-quality biological control approaches, with root diseases especially. And we’re focused on helping growers establish the best plant quality early on.

GM: What products would you recommend from BioWorks?

JL: We have a number of products, but the most popular and well-known are the biofungicides under the RootShield brand. We have RootShield and RootShield PLUS+ and they work at the root level to protect the young plants right from the start and over several weeks. An additional product that is also well-known is Cease, which is a beneficial bacterium that works in a similar fashion. It offers biological control protection of young plants, as well as when it’s transplanted up into finished sizes.

GM: How do these solutions attack root infecting diseases?

JL: Under the RootShield brand, we have strains of beneficial fungi that essentially work collaboratively with the plant. What they do is, they populate the plant root system, but not only does it provide a protective shield of microbial growth — which is friendly to the plant roots and inhibits other pathogens from infecting these root tissues — it also provides what we call a collaborative or symbiotic system at the root zone where plants can improve nutrient uptake with these microbes existing in the root zone. So there’s a dual approach going on with these beneficial fungi. It’s a similar mode of action when it comes to Cease as well. These products also make a lot of sense when it comes to utilizing living organisms. They are friendly to plants and provide a lot of additional benefits besides protection against disease pathogens.

Greenhouse Management: How can shipping put plants at risk?

Paul Pilon: A lot of things can go wrong during shipping. Many transport vehicles often aren’t temperature controlled — there’s high humidity, lower light and the length of time a plant is in that environment varies. A plant could be there anywhere from one day to three or four days, possibly even longer. In some instances, plants are harvested a day or a two before they’re loaded onto a truck adding onto the potential time shipping issues can arise. During this time, plants are not in their natural growing environments, so they are being set up for shipping stresses like ethylene release or diseases such as Botrytis.

GM: How can using a PGR help?

PP: When they are used during production, it not only results in a more compact, aesthetically pleasing plant, but PGRs can also help improve shelf life. Plants that have been treated with PGRs typically have thicker stems and thicker cell walls, so they are going to be less prone to some of these shipping issues. I often see treated plants holding up for almost two weeks longer than they would otherwise. This is especially important in the spring when sales can be halted due to cold, wet weather. OHP has Pac O, Cycocel and B-Nine WSG in its portfolio.

GM: How can wetting agents help address some of these problems?

PP: Wetting agents are compounds that help the growing mix hold onto moisture better, so it lengthens the time between irrigation cycles. Some growers are adding wetting agents to their irrigation to help them maximize their watering practices. The wetting agent OHP offers is Suffusion. During production, wetting agents typically last six to eight weeks and their efficacy lessens over time. It’s helpful to add a wetting agent just prior to shipping to replenish the soil and bring it back up to peak efficacy. The plants will then be at optimal moisture during shipping so they won’t dry out and also helps irrigation management at retail locations. Wetting agents don’t have to be applied the day of shipping, I like to apply them a week or so before to allow them to settle in an reach their full potential prior to shipping.

GM: How can fungicides help?

PP: Growers should apply fungicides preventatively before shipping. It’s important for the fungicide to be there to protect plants before they are placed in adverse conditions during shipping. We have a fungicide called Astun, which is a very good product for growers to apply a day or two before shipping to lessen the occurrence of Botrytis during transit. Last April, I did a shipping trial with Astun on annuals and I evaluated disease development and plant quality prior to and again when unboxing them. Treated plants either had no Botrytis or significantly less vs. untreated plants. The other interesting observation was that on certain crops, there were less stress symptoms. With geraniums, they commonly turn yellow when left in a box during shipping, it was very apparent that plants treated with Astun had significantly less yellowing. We are looking into why this occurs and for other practical applications for growers to use Astun.